I have 3 sonoff devices. When I received them they worked very well (firmware 1.2.0). Easy wifi connect and reconnect! The app shows strong signal on all sonoff.
I firmware updated 1 of them to ver. 1.5.2. Now wifi connection is very weak! Only if I move the sonoff close to my wifi router, it will connect and reconnect automatic!
There must be a bug in the new firmware. Please fix and put out a new firmware..
Check the device if it is shown as SonOff or S20.
Mine showed up as S20 and it updated to 1.5.2.
Other devices are showing up as SonOff and latest firmware are 1.2.0.
I asked the support but they say it has only few difference therefore it's no problem.
Support won't help you on this problem it seems.
It's pretty lame to have a device shown as different model, but that's the quality of itead I suppose.